The upgrading of atmospheric and vacuum residual oils (resids) to lighter, more valuable products has been accomplished by thermal cracking processes such as visbreaking and coking. In visbreaking, a vacuum resid from a vacuum distillation column is sent to a visbreaker where it is thermally cracked. The process conditions are controlled to produce the desired products and minimize coke formation. Vacuum gas oils from the vacuum distillation column are typically sent directly to a fluidized catalytic cracking (FCC) unit. The products from the visbreaker have reduced viscosity and pour points, and include naphtha, visbreaker gas oils and visbreaker residues. The bottoms from the visbreaker are heavy oils such as heavy fuel oils. Various processing schemes have been incorporated with visbreakers. The amount of conversion in visbreakers is a function of the asphaltene and Conradson Carbon Residue (or “CCR”) content of the feed. Generally, lower levels of asphaltene and CCR content in the hydrocarbon feed are favorable to visbreaking. Higher values of asphaltene and CCR content lead to increased coking and lower yields of light liquids.
Petroleum coking relates to processes for converting resids to petroleum coke and hydrocarbon products having atmospheric boiling points lower than that of the feed. Some coking processes, such as delayed coking, are batch processes where the coke accumulates and is subsequently removed from a reactor vessel. In fluidized bed coking, for example fluid coking and FLEXICOKING® (available from ExxonMobil Research and Engineering Co., Fairfax, Va.), lower boiling products are formed by the thermal decomposition of the feed at elevated reaction temperatures, typically from about 480 to 590° C. (896 to 1094° F.), using heat supplied by burning some of the fluidized coke particles.
Following coking, the lower boiling hydrocarbon products, such as coker gas oil, are separated in a separation region and conducted away from the process for storage or further processing. Frequently, the separated hydrocarbon products contain coke particles, particularly when fluidized bed coking is employed. Such coke particles may range in size upwards from submicron to several hundred microns in diameter, but typically are in the submicron to about 50 micron diameter range. It is generally desirable to remove particles larger than about 25 microns in diameter to prevent fouling of downstream catalyst beds used for further processing. Filters, located downstream of the separation zone, are employed to remove coke from the products. Solid hydrocarbonaceous particles present in the separated lower boiling hydrocarbon products may physically bind to each other and the filters, thereby fouling the filter and reducing filter throughput. Fouled filters must be back-washed, removed and mechanically cleaned, or both to remove the foulant.
There is a need in the industry for improved processes for treating high boiling range hydrocarbon feeds such as vacuum gas oils in order to increase the production of distillate boiling range products produced from these hydrocarbon feeds.